| This paper used high-speed video camera and numerical methods investigated the flow boiling heat transfer, and the bubble nucleation, growth, departure in onset and full developed subcooled boiling in high pressure, experimentally and theoretically studied the subcooled flow boiling heat transfer characteristic in narrow rectangular channel.Used high-speed video camera visualization method, investigated the subcooled boiling heat transfer and bubble behaviors in narrow rectangular channel in high pressure for the first time. Found that because the narrowness of the channel, compared with large channel, there have a great difference in bubble behavior and relative character, when used Bowering relation to predict theONB point, this paper given a correlation of C1 = 103.736 Res -0.8 Eu-0.123 to modify theBowering relation to consider the influence of flow velocity and pressure on ONB point.Through high-speed video method, revealed that when bubble be in initial stage of growth, the diameter is very small, about 0.01mm, observed that the stand-on time on heating wall less than 0.5ms, slip and grow on wall with low velocity less than 0.1 m/s. Operating condition such as heat flux, pressure, subcooled temperature of main flow and mass rate of flow notablely influence on the bubbles on initial stage of growth. Among them, the heat flux is the main parameter, with more high heat flux, more advanced ONB point taking place. The influence of the main flow subcooled temperature on bubble behavior and pattern was great, with other conditions keep constant, the main flow subcooled temperature determined the behavior and pattern of bubbles. With difference bubble diameter, the slip velocity is different, the velocity of small bubbles (d=0.01~0.07mm) was between 0.1 to 0.2m/s, and relative big bubbles' (d=0.1~0.3mm) was between 0.25 to 0.5 m/s. In the subcooled liquid flow, bubbles' condensation velocity was between 0.001 to 0.006m/s. From the results gotten from high-speed video, discovered that the process of big bubbles coalesced small bubbles is the main pattern of bubble growing to big bubble and even to vapor layer.In addition, experimental investigated the boiling heat transfer performance of the vertical narrow rectangular channels, got a relation to predict the subcooled flow boiling of-3.7 . Used theoretically method,analyzed the saturated flow boiling in narrow rectangular channel for the first time, simplified the heat transfer characteristic after the NVG point of the channel, got the half-experiential relation about saturated flow boiling in narrow channel of NuH = e6.57Ar1/3 Res0.4359 Pr0.3428. With thedecreasing of cross-section subcooled temperature, and the increasing of mass rate of flow andpressure, the boiling heat transfer coefficient increased. Compared with the Gungor relation used to calculate the subcooled boiling heat transfer of large-scale smooth tube and annular channel, the heat transfer was enhanced notably; the heat transfer enhancement factor was 1.3 to 2.1.Considered that the investigation about the flow pattern related problem in narrow rectangular channel such as large-scale bubbles and vapor-phase coalescence, should under single wall heating condition. This paper investigated the heating method influence upon flow boiling in narrow rectangular channel. Discovered the influence of the single and double heating method was very great upon on boiling. In constant heat flux, the super-saturated temperature of wall with double heating was higher than single one in ONE point, with the increasing of heat flux, the difference become more notable; with constant cross-section subcooled temperature, the qONB of the single-wall heated channel was far higher than double one, with the decreasing of the subcooled temperature, the trendcy was closing. The heating method also influenced on the heat transfer coefficient, with the increasing of heat flux, the average heat transfer coefficient increased, and the slope of the single heating was steeper. In same opera...
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